In recent years, Wi-Fi Direct as an interterminal communication scheme attracts attention from the viewpoint of broadband, enhanced security, and so on. A previous Wi-Fi network operates in an infrastructure mode with a specific device as an access point (AP). On the other hand, in a network conforming to Wi-Fi Direct, any P2P terminal, not a specific device, becomes an owner of a group, thereby enabling communication within the group (for example, see Non-Patent Document 1). A group owner is a P2P terminal operating as an access point of a group and, as a parent of the group, can form a group including another P2P terminal as a child (a client).
Within a P2P group formed in this manner, data can be transferred at high speeds between terminals without connecting to the Internet or the like. In particular, Wi-Fi Direct supports a robust security protocol, and therefore, can realize higher security than a conventional ad hoc mode (IBSS: Independent Basic Service Set, or the like).
However, in the wireless P2P network mentioned above, each group is independently formed and operates, so that communication is restricted within the group. Moreover, in general, the maximum number of terminals in one group has a physical upper limit. For example, in a case where Wi-Fi Direct is implemented with the use of an inexpensive wireless LAN device, the number of terminals in one group is limited to the upper limit of 5 to 10 supported by the device. Such group size limitation restricts message sharing only to the terminals in one group and hampers information sharing in a larger network including a plurality of groups. In the wireless P2P network mentioned above, it is impossible to notify, for example, disaster information, traffic information, SOS signals, voice signals or the like having urgency beyond a local group.
In view of such circumstances, Non-Patent Document 2 proposes a method of communicating between groups via a delivery node. In the communication method described in Non-Patent Document 2, a group owner of a first group selects one or a plurality of client nodes of the first group as delivery nodes. Then, the delivery node disassociates itself from the first group to connect to a group owner of a second group existing nearby, and transmits and receives information to and from the group owner of the second group. A mechanism that a delivery node disassociates itself from a currently connected group and connects to another group is called “switching.” The delivery node periodically performs switching between the first group and the second group, whereby the group owner of the first group and the group owner of the second group can bidirectionally convey information via the delivery node.
On the other hand, the following technique is proposed in relation to the present invention.
Patent Document 1 proposes a switch system that includes one or more ports on a switch configured to transmit an encapsulated packet in accordance with the TRILL protocol. Moreover, it is described in the paragraph 0106 of Patent Document 1 that it is possible to link a set of VMs (virtual machines) in a network with one port profile to group them. This grouping is grouping VMs all connected to the same VLAN and has a different concept from the group formed in the wireless P2P network.
Patent Document 2 proposes an information sharing system that can realize both proper confidential information sharing and ordinary broad information sharing within a group of users existing at remote places. However, a terminal does not perform switching between groups.
Patent Document 3 describes a method of constructing a VPN (Virtual Private Network) to realize communication between hosts. For example, a tunnel connection considering security is set up between networks where a VPN is constructed. For example, in a case where, in a connection configuration of PC (personal computer) 1—GW (gateway) 1—GW 2—PC 2, a VPN is configured with the use of the PC 1 and the PC 2, a tunnel connection is set up between the GW 1 and the GW 2. Then, communication between the hosts is realized by IP routing using a temporary IP address. However, Patent Document 3 does not describe a tunnel connection in a case where there is no fixed communication path between GW 1 and GW 2.
Patent Document 4 proposes a data communication apparatus that includes a congestion detection means. The congestion detection means determines whether or not the amount of data continuously transmitted from a transmission terminal is close to a continuously receivable data size notified to the transmission terminal and, if determining it is close, determines whether or not the continuously receivable data size can be increased and, if determining it can be increased, increases the continuously receivable data size and determines whether or not congestion has occurred while receiving data. When congestion is detected, the data communication apparatus reduces the continuously receivable data size and returns a response acknowledgement.    Patent Document 1: Japanese Translation of PCT Application Publication JP-A 2013-526234    Patent Document 2: Re-publication of PCT Publication WO 2006/059639    Patent Document 3: Japanese Unexamined Patent Application Publication JP-A 2008-092170    Patent Document 4: Japanese Unexamined Patent Application Publication JP-A 2000-174812    Non-Patent Document 1: Wi-Fi Alliance Technical Committee PSP Task Group, Wi-Fi Peer-to-Peer (P2P) Technical Specification Version 1.1    Non-Patent Document 2: Chaki Prakash, Masato Yasuda, Kazuaki Nakajima, “Dynamic Topology Reformation for Content Dissemination in Wi-Fi Peer-to-Peer Networks,” the Institute of Electronics, Information and Communication Engineers, Feb. 24, 2015, Proceedings of the 2015 IEICE General Conference BS-3-53
However, the delivery node cannot simultaneously connect to both the first group and the second group. When connecting, the delivery node connects to only one of the groups. Thus, the delivery node becomes an end point of a communication path. Therefore, a wireless terminal belonging to the first group and a wireless terminal belonging to the second group cannot directly communicate. Such a problem is hard to solve even by combining the techniques described in Patent Documents 1 to 5 and Non-Patent Documents 1 and 2.